Auto-injector

ABSTRACT

According to the invention, an auto-injector for administering a dose of a liquid medicament (M) comprises of a substantially cylindrical housing arranged to contain a pre-filled syringe; a syringe retainer slidably arranged with respect to the housing that mounts a pre-filled syringe with an injection needle, a plunger and a stopper for sealing a syringe barrel of the pre-filled syringe; a coupling shroud slidably arranged within the housing and releasably coupled to the plunger; and a single drive means. Upon release, the single drive means is capable of driving the coupling shroud in the proximal direction (P). The proximal translatory movement of the coupling shroud with respect to the housing, translates the syringe retainer in the proximal direction (P) to expose the injection needle of the pre-filled syringe, depresses the plunger connected to the stopper into the syringe barrel to expel the dose of medicament (M) and advances a needle shroud to a safe position (PS) to surround the injection needle after the medicament (M) has been at least partially delivered. The coupling shroud is decoupled from the plunger at a pre-determined second position (II) defined by an aperture formed into the housing.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase Application pursuant to35 U.S.C. §371 of International Application No. PCT/EP2011/073503 filedDec. 21, 2011, which claims priority to European Patent Application No.10196068.0 filed Dec. 21, 2010 and U.S. Provisional Patent ApplicationNo. 61/432,254, filed Jan. 13, 2011. The entire disclosure contents ofthese applications are herewith incorporated by reference into thepresent application.

TECHNICAL FIELD

The invention relates to an auto-injector for administering a dose of aliquid medicament.

BACKGROUND

Administering an injection is a process which presents a number of risksand challenges for users and healthcare professionals, both mental andphysical.

Injection devices (i.e. devices capable of delivering medicaments from amedication container) typically fall into two categories—manual devicesand auto-injectors.

In a manual device—the user must provide the mechanical energy to drivethe fluid through the needle. This is typically done by some form ofbutton/plunger that has to be continuously pressed by the user duringthe injection. There are numerous disadvantages to the user from thisapproach. If the user stops pressing the button/plunger then theinjection will also stop. This means that the user can deliver anunderdose if the device is not used properly (i.e. the plunger is notfully pressed to its end position). Injection forces may be too high forthe user, in particular if the patient is elderly or has dexterityproblems.

The extension of the button/plunger may be too great. Thus it can beinconvenient for the user to reach a fully extended button. Thecombination of injection force and button extension can causetrembling/shaking of the hand which in turn increases discomfort as theinserted needle moves.

Auto-injector devices aim to make self-administration of injectedtherapies easier for patients. Current therapies delivered by means ofself-administered injections include drugs for diabetes (both insulinand newer GLP-1 class drugs), migraine, hormone therapies,anticoagulants etc.

Auto-injectors are devices which completely or partially replaceactivities involved in parenteral drug delivery from standard syringes.These activities may include removal of a protective syringe cap,insertion of a needle into a patient's skin, injection of themedicament, removal of the needle, shielding of the needle andpreventing reuse of the device. This overcomes many of the disadvantagesof manual devices. Injection forces/button extension, hand-shaking andthe likelihood of delivering an incomplete dose are reduced. Triggeringmay be performed by numerous means, for example a trigger button or theaction of the needle reaching its injection depth. In some devices theenergy to deliver the fluid is provided by a spring.

US 2002/0095120 A1 discloses an automatic injection device whichautomatically injects a pre-measured quantity of fluid medicine when atension spring is released. The tension spring moves an ampoule and theinjection needle from a storage position to a deployed position when itis released. The content of the ampoule is thereafter expelled by thetension spring forcing a piston forward inside the ampoule. After thefluid medicine has been injected, torsion stored in the tension springis released and the injection needle is automatically retracted back toits original storage position.

SUMMARY

It is an object of the present invention to provide an improvedauto-injector.

The object is achieved by an auto-injector according to claim 1.

Preferred embodiments of the invention are given in the dependentclaims.

In the context of this specification, the terms distal and proximal aredefined from the point of view of a person receiving an injection.Consequently, a proximal direction refers to a direction pointingtowards the body of a patient receiving the injection and a proximal enddefines an end of an element that is directed towards the body of thepatient. Respectively, the distal end of an element or the distaldirection D is directed away from the body of the patient receiving theinjection and opposite to the proximal end or proximal direction.

According to the invention, an auto-injector for administering a dose ofa liquid medicament comprises

-   -   a substantially cylindrical housing arranged to contain a        pre-filled syringe,    -   a syringe retainer slidably arranged with respect to the housing        that mounts a pre-filled syringe with an injection needle, a        plunger and a stopper for sealing a syringe barrel of the        pre-filled syringe,    -   a coupling shroud slidably arranged within the housing and        releasably coupled to the plunger and    -   a single drive means. Upon release, the single drive means is        capable of driving the coupling shroud from a first position in        the proximal direction. The proximal translatory movement of the        coupling shroud with respect to the housing    -   translates the syringe retainer in the proximal direction to        expose the injection needle of the pre-filled syringe,    -   depresses the plunger connected to the stopper into the syringe        barrel to expel the dose of medicament and    -   advances a needle shroud to a safe position to surround the        injection needle after the medicament has been at least        partially delivered. The coupling shroud is decoupled from the        plunger at a pre-determined second position defined by an        aperture formed into the housing.

The mechanism of the auto-injector is arranged in a manner that aplurality of functions is executed by the single drive means. Theinjection needle is inserted into the skin of the patient, the plungeris translated to expel the medicament and the needle shroud is movedproximally to provide needle safety after the injection is completed bythe action of the spring means. Conventional auto-injectors usuallycomprise a plurality of spring means to accomplish these tasks. Theauto-injector according to the invention comprises only few parts and isparticularly inexpensive to mass-produce. Consequently, theauto-injector is particularly suited as a single-use device that may bedisposed after an injection has been carried out.

The coupling shroud is initially coupled to the plunger to translate thesyringe retainer proximally, whereby the injection needle is insertedinto the skin of the patient, and to depress the stopper into thesyringe barrel to expel the medicament. A crucial step for designing theauto-injector with the single drive means is the decoupling of theplunger and the coupling shroud at the proper pre-determined secondposition, so that the same drive means may be used to advance the needleshroud after the medication has been completely or partially delivered.The pre-determined second position is defined by a longitudinal aperturein the housing.

In one possible embodiment of the invention, the pre-determined secondposition defined by the aperture is arranged in a manner that allows fora decoupling of the plunger from the coupling shroud before the stopperreaches a proximal end of the syringe barrel. This ensures that areliable activation of the safety functions of the auto-injector areactivated after the medicament has been at least partially delivered.

According to another possible embodiment of the invention, a couplingcatch is arranged to abut against a shoulder formed to the plunger as aparticularly simple and reliable means to releasably couple the plungerto the coupling shroud. The coupling shroud is moved by the action ofthe relaxing drive means in the proximal direction and coupled to theplunger connected to the stopper to insert the injection needle beforethe injection and to expel the medication during the injection.

The aperture formed into the lateral side of the housing at the secondposition allows the coupling catch to deflect radially outwards at thesecond position, so that the coupling shroud is decoupled from theplunger after the medicament is partially or completely delivered.

Preferably, the single drive means is arranged as a single compressionspring. Compression springs are readily available and inexpensive drivemeans that may be used to cut down on production costs.

According to one possible embodiment of the invention, a rotating collaris rotatably arranged within the housing. The rotating collar createsfriction to slow down a proximal movement of the needle shroud that isdesigned to rest onto the skin of the patient during the injection. Therotating collar acts as a dampening element that alleviates the pressureexerted upon the skin of the patient by the single drive means via theneedle shroud and thus reduces the risk of injuries like bruises.Furthermore, the modulus of resilience of the single drive means may bechosen to be sufficiently large without having to worry about potentialinjury risks. Thus, the modulus of resilience of the single drive meansis adapted to reliably provide an energy supply for a plurality ofactions comprising, in particular, the advancing of the syringe retainerand the needle shroud, the displacement of the stopper to expel themedication and the decoupling of the plunger and the coupling shroud.

Preferably, the rotating collar comprises a pin that engages a helicalrecess formed into the needle shroud. The engagement of the helicalrecess and the pin forces the rotating collar to rotate around theneedle shroud when the needle shroud is translated. This in particulardampens a proximal movement of the needle shroud and thus reduces thepressure exerted upon the skin of the patient by generating friction.

According to another possible embodiment of invention, the auto-injectorcomprises safety means that are arranged to cooperate with the needleshroud to prevent a release of the drive means when the needle shroud isin an advanced position and hence is not pushed against the skin of thepatient at the injection site. This mechanism avoids an early release ofthe drive means and thus a prematurely expelling of the medicament.Furthermore, injuries resulting from an activation of the drive meanswhen the auto-injector is not or not properly placed onto the skin ofthe patient are reduced.

In one possible embodiment of the invention, the safety means comprisesan elastic bushing that engages the plunger and/or the coupling shroud.The elastic bushing is firmly attached to a proximal end of the housingand may engage the coupling shroud and/or the plunger to prevent aninadvertent release of the drive means.

In another possible embodiment of the invention, a release element ishinged to the lateral side of the housing. The safety means comprises ablocking element slidably arranged relative to the housing. Manualactuation of the release element causes the release element to pivotabout a hinge to release the drive means. The blocking element isarranged to limit a pivoting movement of the release element when theneedle shroud is in an advanced position and hence to prevent anactivation of the drive means. The release element is allowed pivotabout the hinge when the needle shroud is moved to a refracted positionby pressing the needle shroud against the skin surface of the patientreceiving the injection.

Preferably, the blocking element is arranged to block a distal movementof the needle shroud when the release element is manually actuated whilethe needle shroud is located in the advanced position. The pivotingrelease element may comprise an inward projection that is pushed radialinwards by manually actuating the release element to block adisplacement of the needle shroud from the advanced position. The useris thus forced to perform the sequence of actions necessary to start theinjection in the proper order. In particular, the user is forced tofirst push the needle shroud against the skin of the patient totranslate the needle shroud to the retracted position. Subsequently, therelease element is manually actuated to release the drive means.

The auto-injector may preferably be used for subcutaneous orintra-muscular injection, particularly for delivering one of ananalgetic, an anticoagulant, insulin, an insulin derivate, heparin,Lovenox, a vaccine, a growth hormone, a peptide hormone, a proteine,antibodies and complex carbohydrates.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are not limitiveof the present invention, and wherein:

FIGS. 1A and 1B show two different sectional views of an auto-injectoraccording to a first embodiment of the invention with a hinged releaseelement before an injection,

FIG. 2 is an expanded sectional view of the auto-injector according tothe first embodiment, wherein the release element is blocked to preventan inadvertent release of a drive means,

FIG. 3 is an expanded sectional view of the hinged release element thatis actuated to release the drive means,

FIGS. 4A and 4B are two different sectional views of the auto-injectoraccording to the first embodiment after a drug has been delivered,

FIG. 5 is an isometric view of a needle shroud,

FIGS. 6A and 6B are two different sectional views of the auto-injectoraccording to the first embodiment after an injection has been performed,

FIGS. 7A and 7B are two different sectional views of an auto-injectoraccording to a second embodiment of the invention,

FIG. 8 is a sectional view of a distal end section of the auto-injectoraccording to the second embodiment of the invention,

FIGS. 9A and 9B are two different sectional views of an auto-injectoraccording to a third embodiment of the invention,

FIG. 10 is a sectional view of a distal end section of the auto-injectoraccording to the third embodiment of the invention.

Corresponding parts are marked with the same reference symbols in allfigures.

DETAILED DESCRIPTION

FIGS. 1A and 1B show two sectional views of an essentially cylindricalauto-injector 1 according to a first embodiment of the invention,wherein the sectional plane shown in FIG. 1A is oriented perpendicularlyto the one shown in FIG. 1B. The auto-injector 1 comprises a housing 2,a proximal needle shroud 3, a syringe retainer 4 adapted to mount andmove translatably with a pre-filled syringe 5 within the housing 2, acoupling shroud 6 slidably arranged within the housing 2 and a releaseelement 7 hinged to a lateral side of the substantially cylindricalhousing 2 of the auto-injector 1.

A single drive means 8 is arranged between the distal end of the housing2 and the coupling shroud 6 to bias the coupling shroud 6 in a proximaldirection P towards the skin of a patient receiving an injection.

According to one possible embodiment of the invention, the drive means 8is arranged as a single, conventional compression spring.

The coupling shroud 6 is releasably coupled to a plunger 9 that isconnected to a stopper 10 fluid-tightly sealing a distal end of asyringe barrel 11 containing a dose of a medicament M. An inner cavityof the syringe barrel 11 is in fluid communication with an injectionneedle 12, so that the dose of the medicament M may be expelled throughthe injection needle 12 by displacing the stopper 10 in the proximaldirection P.

Before the injection, the coupling shroud 6 abuts against a distal endof the release element 7 to releasably retain the coupling shroud 6 in afirst position I, wherein the coupling shroud 7 is located at a distalend of the housing 2. The drive means 8 is compressed, so that thecoupling shroud 6 is strongly biased in the proximal direction P.

The plunger 9 extends from the syringe barrel 11 in a distal direction Dand comprises a shoulder 9.1 of increased diameter. The coupling shroud6 comprises an inwardly protruding coupling catch 6.1 that bears againstthe shoulder 9.1 so that the plunger 9 and the coupling shroud 6 may bejointly moved in the proximal direction P by the action of the relaxingdrive means 8.

The proximal end of the needle shroud 3 is designed to be pushed againstthe skin surface of the patient during the injection. Edges of theneedle shroud 3 may thus be smoothed to avoid injuries. The needleshroud 3 is slidably arranged within the housing 2 of the auto-injector1, so that the needle shroud 3 may be pushed from an advanced positionPA shown in FIGS. 1A and 1B in the distal direction D. A biasing means13 bears against the needle shroud 3 and the housing 2 to bias theneedle shroud 3 towards the advanced position PA.

An annular rotating collar 14 engages an outer surface of the needleshroud 3. The rotating collar 14 rotates around an axis of thesubstantially cylindrical auto-injector 1 when the needle shroud 3 islongitudinally displaced in the proximal and/or the distal direction P,D. The rotating collar 14 acts as a damping means that creates frictionto slow down the movement of the needle shroud 3 and to reduce thepressure exerted onto the skin of the patient receiving the injection.

The release element 7 hinged to the housing 2 works like a see-saw: aproximal section may be pushed radially inwards, whereby the releaseelement 7 pivots about a hinge 15, so that the distal section of therelease element 7 moves radially outwards and the coupling shroud 6 isdisengaged to release the drive means 8.

The auto-injector 1 comprises safety means S that prevents an earlyrelease of the drive means 8. The safety means S ensures that the needleshroud 3 is pushed against the skin of the person receiving theinjection before the drive means 8 may be released.

According to the first embodiment of the invention, the safety means Scomprises a blocking element 16 slidably arranged with the housing 2.When the needle shroud 3 is positioned in the advanced position PA, theblocking element 16 is positioned to prevent a pivoting movement of therelease element 7 and thus a release of the coupling shroud 6. Aradially outwards protruding blocking projection 16.1 of the blockingelement 16 is located opposite to an inward protrusion 7.1 formed to therelease element 7. If the proximal section of the release element 7 ispushed inwards, the inward protrusion 7.1 abuts against the blockingprojection 16.1 to limit the pivoting movement of the release element 7,so that a release of the coupling shroud 6 and the drive means 8 isprevented.

FIG. 2 shows a proximal section of the auto-injector 1 in a sectionalview with the blocking element 16 positioned to prevent an inadvertentactuation of the hinged release element 7 to release the drive means 8.

A distal end of the needle shroud 3 is clipped to the housing 2 andretained between two inwardly protruding retaining protrusions 2.1formed into an inner surface of the housing 2. The two retainingprotrusions 2.1 are longitudinally displaced from each other to limitthe range of axial displacement of the needle shroud 3 with respect tothe housing 2. A boss 3.1 formed into an outer surface of the needleshroud 3 bears against an inner surface of the blocking element 16, sothat the blocking element 16 may move with the needle shroud 3 in theproximal direction P to deblock the release element 7.

The blocking projection 16.1 comprises a central indention that forces auser of the auto-injector 1 to perform a sequence of actions necessaryto inject the dose of the medicament M in the proper order. If therelease element 7 is pushed inwards before the needle shroud 3 is movedproximally from the advanced position PA towards a retracted position PR(see FIG. 3) by pushing the needle shroud 3 towards the skin of thepatient, the inward projection 7.1 is retained in the centralindentation of the blocking projection 16.1, so that both thelongitudinal displacement of the needle shroud 3 and the pivotingmovement of the release element 7 is blocked.

A proper sequence of actions for injecting the dose of the medicament Mis described in the following. First, the user pushes the needle shroud3 against the skin to move the needle shroud 3 distally to the retractedposition PR illustrated in FIG. 3. The blocking element 16 jointly moveswith the needle shroud 3 in the distal direction D, so that the releaseelement 7 may be manually actuated to pivot about the hinge 15, wherebythe drive means 8 are released.

Upon release of the drive means 8, the coupling shroud 6 is urged in theproximal direction P. The single and fully compressed drive means 8drives the coupling shroud 6 and the plunger 9 coupled thereto in theproximal direction P. The coupling shroud 6 first pushes the syringeretainer 4 by means of plunger 9, stopper 10 and the friction betweenstopper 10 and syringe 11 proximally to insert the injection needle 12into the skin of the patient and a first clip connection 2.2 formed intoa lateral side of the housing 2 latches to an outward protrusion 4.1 ofthe syringe retainer 4, as illustrated in more detail in FIG. 4B.

The syringe retainer 4 and the pre-filled syringe 5 mounted thereto isnow locked to the housing 2. The coupling shroud 6 is moved further inthe proximal direction P by the action of the relaxing drive means 8,whereby the plunger 9 is depressed into the syringe barrel 11 to expelthe dose of the medicament M contained therein through the injectionneedle 12.

FIGS. 4A and 4B show two sectional views of the auto-injector 1according to the first embodiment of the invention with the plunger 9fully depressed within the syringe barrel 11. The dose of the medicamentM has been delivered beneath the skin of the patient. The couplingshroud 6 is located in an intermediate second position II. The drivemeans 8 is not yet completely discharged and biases the coupling shroud6 in the proximal direction P. The shoulder 9.1 engages a ramp of thecoupling catch 6.1 to deflect the coupling catch 6.1 in a radial outwarddirection. An aperture 2.3 is formed into the housing 2 to allow for aradial outward deflection of the coupling catch 6.1, so that thecoupling catch 6.1 overcomes the shoulder 9.1 decoupling the couplingshroud 6 from the plunger 9.

In a possible embodiment of the invention, the aperture 2.3 defining thesecond position II is located at a longitudinal position along thehousing 2 that allows for a full depression of the plunger 9 completelyemptying the syringe barrel 11 before the plunger 9 is decoupled fromthe coupling shroud 6.

Alternatively, the aperture 2.3 defining the second position II may belocated at a longitudinal position along the housing 2 that allows foran adjustment space accounting for manufacturing tolerances. Theadjustment space is dimensioned as to allow for a reliable decoupling ofthe plunger 9 from the coupling shroud 6 even if the parts constitutingthe auto-injector 1 comprise mismatch in mould or are slightlymisaligned. In this alternative embodiment, the dose of the medicament Mmay or may not be completely expelled before the plunger 9 is decoupledfrom the coupling shroud 6.

The retaining protrusions 2.1 are elastically supported and may bedeflected radially outwards to release the needle shroud 3. The couplingshroud 6 engages a ramp of the retaining protrusions 2.1 and splays theretaining protrusions 2.1 outwards, whereby the needle shroud 3 isreleased and allowed to move proximally from the retracted position PRtowards an extended safe position PS.

The drive means 8 is still partially loaded when the coupling shroud 6is located in the second position II. In a possible embodiment of theinvention the biasing force of the drive means 8 exerted on the couplingshroud 6 in the second position II is about 10 N.

The coupling shroud 6 bears against a distal end of the needle shroud 3,so that the needle shroud 3 may be moved to the safe position PS by theaction of the further relaxing drive means 8. As the biasing forceexerted onto the needle shroud 3 by the drive means 8 may be relativelylarge and could even bruise the patient, the rotating collar 14 isarranged within the housing 2 to partially absorb the excess energy ofthe drive means 8 and slow down the proximal movement of the needleshroud 3 by generating friction.

FIG. 5 shows an isometric view of the needle shroud 3. A helical recess3.2 is formed into a tubular proximal section 3.3 of the needle shroud3. The proximal section 3.3 of the needle shroud 3 is inserted into theannular rotating collar 14, wherein a pin 14.1 formed to an innersurface of the rotating collar 14 protrudes into the helical recess 3.2as shown in FIG. 6A. The linear translatory movement of needle shroud 3towards the safe position PS thus causes the rotating collar 14 torotate within the housing 2 around the axis of the auto-injector 1.

FIGS. 6A and 6B show two different sectional views of the auto-injector1 according to the first embodiment of the invention after the injectionhas been performed. The needle shroud 3 is permanently locked to thesafe position PS by a second clip connection 2.4 formed into the housing2. The needle shroud 3 surrounds the injection needle 12 and extends asuitable distance proximally beyond the needle tip to avoid accidentalneedle stick injuries after the auto-injector 1 has been used.

FIGS. 7A and 7B show two different sectional views of an auto-injector 1according to a second embodiment of the invention before the injection.The sectional plane shown in FIG. 7A is oriented perpendicularly to thesectional plane shown in FIG. 7B.

The needle shroud 3 of the auto-injector 1 according to the secondembodiment substantially extends over the axial length of the housing 2.Before the injection, the needle shroud 3 is mounted to the housing 2 bythe retaining protrusions 2.1 that protrude into orifices formed into alateral side of the needle shroud 3. The orifices comprise alongitudinal length that allows the needle shroud 3 to be slid from theadvanced position PA to the retracted position PR.

A retaining catch 2.5 is formed to an inner surface of the housing 2 andprotrudes through an opening formed into the needle shroud 3 toreleasably mount the syringe retainer 4 retaining the pre-filled syringe5. The retaining catch 2.5 comprises a bevelled ramp and is deflectablein a radial outward direction. The retaining catch 2.5 latches to theoutward protrusion 4.1 formed to the outer surface of the syringeretainer 4 when the needle shroud 3 is in the advanced position PA

The needle shroud 3 abuts against the bevelled ramp of the retainingcatch 2.5 when the needle shroud 3 is moved from the advanced positionPA in the distal direction D, whereby the retaining catch 2.5 isdeflected in a radial outward direction and disengages the outwardprotrusion 4.1, so that the syringe retainer 4 may be moved in theproximal direction P.

The release element 7, shown in more detail in FIG. 8, is arranged as apush button and mounted to a distal end of the housing 2. The releaseelement 7 may be pushed in the proximal direction P to release the drivemeans 8 when the needle shroud 3 is in the retracted position PR,whereas the release element 7 and thus the release of the drive means 8is blocked when the needle shroud 7 is in the advanced position PA.

According to the second embodiment of the invention, the safety means Sthat prevent the early release of the drive means 8 comprises clips 2.6that may deflect in a radial outward direction and a bushing 17 lockingthe plunger 9 before use of the auto-injector 1.

Before the auto-injector 1 is used, the clips 2.6 formed to the housing8 latch to the release element 7. (See FIG. 7 b) The clips 2.6 block themovement of the release element 7 in the proximal direction P, so that amanual actuation of the release element 7 is prevented as long as theneedle shroud 3 is in the advanced position PA. A distal movement of therelease element 7 is blocked by a first detent 2.7 engaging an innersurface of the release element 7.

The clip 2.6 comprises a ramp that the needle shroud 3 engages whenpushed distally from the advanced position PA to the refracted positionPR, whereby the clip 2.6 is deflected radially outwards to disengage theneedle shroud 3. The release element 7 may be pushed in the proximaldirection P when the needle shroud 3 is in the retracted position PR.

The plunger 9 comprises a distal end 9.2 of increased diameter that isretained in the bushing 17 firmly attached to a distal end of thehousing 2. The bushing 17 comprises an inner surface corresponding tothe distal end 9.2 of the plunger 9 that engages the distal end 9.2 in alocked position L to lock the plunger 9 and the coupling shroud 6coupled thereto to the housing 2 before use of the auto-injector 1. Thebushing 17 abuts radially against an annular inner collar 7.2 of therelease element 7 in the locked position L shown in FIGS. 7A and 7B. Aradial outward deflection of the bushing 17 releasing the plunger 9 isthus prevented.

FIG. 8 shows a sectional view of a distal end section of theauto-injector 1 according to the second embodiment of the invention. Theneedle shroud 3 is located in the retracted position PR and the releaseelement 7 is pushed in the proximal direction P, so that the bushing 17disengages the annular inner collar 7.2 of the release element 7. Thebushing 17 is positioned in an unlocked position U and may deflectoutwardly to release the plunger 9.

Furthermore, the bushing 17 acts as a counter bearing for the drivemeans 8 bearing against the bushing 17 in the distal direction D.

FIGS. 9A and 9B show two different sectional views of an auto-injector 1according to a third embodiment of the invention, wherein the releaseelement 7 is arranged as an outer sleeve extending over a substantiallength of the auto-injector 1.

According to the third embodiment of the invention, the safety means Sthat prevent the early release of the drive means 8 comprise clips 2.6,second and third detents 2.8, 7.3, a locking catch 6.2 formed to thecoupling shroud 6 and the bushing 17 that comprises an inner sleeve 17.1receiving a lug 7.4, wherein the locking catch 6.2 latches to a collar17.2 of the inner sleeve 17.1.

The release element 7 of the third embodiment is gripped by a user toperform the injection. When the needle shroud 3 is in the advancedposition PA, the proximal displacement of the release element 7 isblocked by the clips 2.6 in a similar manner as in the second embodimentdescribed herein above.

Additionally, the release element is releasably retained in positionbefore the injection by the second and the third detents 2.8, 7.3respectively formed to an outer surface of the housing 2 and to an innersurface of the release element 7, wherein the second and third detents2.8, 7.3 comprise correspondingly shaped ramps facing each other.

The bushing 17 of the third embodiment comprises the inner sleeve 17.1that receives the lug 7.4 formed to an inner surface of the releaseelement 7. A proximal end of the lug 7.4 snugly fits in the centralaperture of the inner sleeve 17.1, so that an inward deflection of theinner sleeve 17.1 is prevented.

The inner sleeve 17.1 comprises a collar 17.2. An inwardly protrudinglocking catch 6.2 of the coupling shroud 6 latches to the collar 17.2before use of the auto-injector 1 to releasably retain the couplingshroud 6 in the first position I.

FIG. 10 shows a sectional view of a distal end section of theauto-injector 1 according to the third embodiment of the invention. Therelease element 7 is actuated and moved in the proximal direction P. Theproximal end of the lug 7.4 disengages the inner sleeve 17.1 of thebushing 17, so that the inner sleeve 17.1 may bend radially inwards,whereby the locking catch 6.2 disengages the collar 17.2 and releasesthe coupling shroud 8 and the drive means 8.

The invention claimed is:
 1. Auto-injector for administering a dose of aliquid medicament (M), comprising: a substantially cylindrical housingarranged to contain a pre-filled syringe, a syringe retainer slidablyarranged with respect to the housing that mounts a pre-filled syringewith an injection needle, a plunger and a stopper for sealing a syringebarrel, a coupling shroud slidably arranged within the housing andreleasably coupled to the plunger and a single drive means capable of,upon release: driving the coupling shroud from a first position (I) inthe proximal direction (P), wherein the proximal translatory movement ofthe coupling shroud with respect to the housing, translates the syringeretainer in the proximal direction (P) to expose the injection needle ofthe pre-filled syringe, depresses the plunger connected to the stopperinto the syringe barrel to expel the dose of medicament (M) and advancesa needle shroud to a safe position (PS) to surround the injection needleafter the medicament (M) has been at least partially delivered, whereinthe coupling shroud is decoupled from the plunger at a pre-determinedsecond position (II) defined by an aperture formed into the housing,wherein a coupling catch is arranged to abut against a shoulder formedto the plunger to releasably couple the plunger to the coupling shroud.2. An auto-injector according to claim 1, wherein the pre-determinedsecond position (II) defined by the aperture is arranged in a mannerthat allows for a decoupling of the plunger from the coupling shroudbefore the stopper reaches a proximal end of the syringe barrel.
 3. Anauto-injector according to claim 1, wherein the aperture allows thecoupling catch to deflect radially outwards to decouple the couplingshroud from the plunger at the second position (II).
 4. An auto-injectoraccording to claim 3, wherein the rotating collar comprises a pin thatengages a helical recess formed into the needle shroud.
 5. Anauto-injector according to claim 1, wherein the single drive means isarranged as a single compression spring.
 6. An auto-injector accordingto claim 1, wherein a rotating collar is rotatably arranged within thehousing for creating friction to slow down a proximal movement of theneedle shroud.
 7. An auto-injector according to claim 1, wherein safetymeans (S) are arranged to cooperate with the needle shroud to prevent arelease of the drive means when the needle shroud is in an advancedposition (PA).
 8. An auto-injector according to claim 7, wherein thesafety means (S) comprise a bushing that engages the plunger and/or thecoupling shroud to prevent the release of the drive means.
 9. Anauto-injector according to claim 7, wherein the safety means (S)comprises a blocking element that is slidably arranged relative to thehousing, wherein the blocking element is arranged to limit a pivotingmovement of a release element hinged to lateral side of the housing whenthe needle shroud is in the advanced position (PA) and wherein theblocking element is arranged to allow the release element to pivot abouta hinge when the needle shroud is in a retracted position (PR).
 10. Anauto-injector according to claim 9, wherein the blocking element isarranged to block a distal movement of the needle shroud when therelease element is manually actuated while the needle shroud is locatedin the advanced position (PA).